Concrete building block



FIG. 1 is a perspective view of a concrete building block showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a left side view thereof;

FIG. 7 is a right side view thereof; and,

FIG. 8 is a cross-sectional view of FIG. 2 thereof.

The broken lines depict portions of the concrete building block which form no part of the claimed design. 

CLAIM The ornamental design for a concrete building block, as shown and described. 